Determination of the radioactive material and plutonium holdup in ducts and piping in the 327 Building

Abstract

The 327 Building Post Irradiation Testing Laboratory is used for temporary storage and for destructive and nondestructive examination of irradiated reactor fuels and structural materials. The facility contains 12 shielded hot cells, two water-filled basins, and dry storage. This report describes the measurements performed to determine the radionuclide content and mass of Pu in ducts, filters, and piping in the basement of the 327 Building at the Hanford Site in Washington State. This information is needed to characterize facility radiation levels, to verify compliance with criticality safety specifications, and to allow more accurate nuclear material control using nondestructive assay (NDA) methods. Gamma assay techniques typically employed for NDA analysis were used to determine the gamma-emitting isotopes in the ducts, filters, and piping. Passive neutron counting was selected to estimate the Pu content because high gamma levels from fission and activation products effectively mask any gamma emissions from Pu. A high-purity gamma-ray detector was used to measure the mixed fission and activation radionuclides. A slab neutron detector containing five {sup 3}He proportional counters was used to determine the neutron emission rates and estimate the mass of Pu present. Estimated Pu mass in the basement ductwork and filters is 7.2 grams. The radioactive liquid waste system line has 4.2 grams and Special Environmental Radiometallurgy Facility cell recirculating system contains 8.7 grams in the lower filter housing and associated piping. Total Pu mass holdup estimates range from 20.1 grams, assuming that the Pu is weapons-grade Pu, to a best estimate of 11.0 grams Pu, assuming 11% {sup 240}Pu.